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The environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin disrupts morphogenesis of the rat pre-implantation embryo.

Hutt KJ, Shi Z, Albertini DF, Petroff BK - BMC Dev. Biol. (2008)

Bottom Line: Additionally, the size, shape and position of nuclei were modified in compaction stage pre-implantation embryos collected from treated animals.We have identified the compaction stage of pre-implantation embryogenesis as critically sensitive to the effects of TCDD, while survival to the blastocyst stage is not compromised.To the best of our knowledge this is the first in vivo study to demonstrate a critical window of pre-implantation mammalian development that is vulnerable to disruption by an AhR ligand at environmentally relevant doses.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Internal Medicine, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA. huttx006@umn.edu

ABSTRACT

Background: Environmental toxicants, whose actions are often mediated through the aryl hydrocarbon receptor (AhR) pathway, pose risks to the health and well-being of exposed species, including humans. Of particular concern are exposures during the earliest stages of development that while failing to abrogate embryogenesis, may have long term effects on newborns or adults. The purpose of this study was to evaluate the effect of maternal exposure to the AhR-specific ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the development of rat pre-implantation embryos with respect to nuclear and cytoskeletal architecture and cell lineage allocation.

Results: We performed a systematic 3 dimensional (3D) confocal microscopy analysis of rat pre-implantation embryos following maternal exposure to environmentally relevant doses of TCDD. Both chronic (50 ng/kg/wk for 3 months) and acute (50 ng/kg and 1 mug/kg at proestrus) maternal TCDD exposure disrupted morphogenesis at the compaction stage (8-16 cell), with defects including monopolar spindle formation, f-actin capping and fragmentation due to aberrant cytokinesis. Additionally, the size, shape and position of nuclei were modified in compaction stage pre-implantation embryos collected from treated animals. Notably, maternal TCDD exposure did not compromise survival to blastocyst, which with the exception of nuclear shape, were morphologically similar to control blastocysts.

Conclusion: We have identified the compaction stage of pre-implantation embryogenesis as critically sensitive to the effects of TCDD, while survival to the blastocyst stage is not compromised. To the best of our knowledge this is the first in vivo study to demonstrate a critical window of pre-implantation mammalian development that is vulnerable to disruption by an AhR ligand at environmentally relevant doses.

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Nuclear profiles of compaction stage pre-implantation embryos from control and acutely exposed animals. Z-series datasets for the DNA channel were compressed into a single plane and 6 randomly selected nuclei (each from a different pre-implantation embryo) for each group (Control and 50 ng/kg and 1 μg/kg TCDD) were compared.
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Figure 4: Nuclear profiles of compaction stage pre-implantation embryos from control and acutely exposed animals. Z-series datasets for the DNA channel were compressed into a single plane and 6 randomly selected nuclei (each from a different pre-implantation embryo) for each group (Control and 50 ng/kg and 1 μg/kg TCDD) were compared.

Mentions: Acute maternal TCDD exposure at the lower dose did not alter the number of compaction stage pre-implantation embryos relative to controls, but only ~52% of pre-implantation embryos from treated animals were normal (Table 1). Exposure to the higher dose of TCDD decreased the number of pre-implantation embryos, and an even lower proportion (~46%) of these pre-implantation embryos were normal (Table 1). A range of defects in nuclear and cytoskeletal integrity were observed (Fig. 3D–L), including a dose dependent loss of microtubule and f-actin staining in some blastomeres (Fig. 3J–L). Additionally, f-actin localization changed from a plasma membrane concentrated (Fig. 3C) to a more diffuse pattern of stain (Fig. 3I and 3L). In pre-implantation embryos from the 1 μg/kg treatment group, blastomeres often exhibited micronuclei (Fig. 3K, arrow) and nuclei of different sizes. Further analyses of nuclear shape revealed a range of profiles deviating from being smooth surfaced in controls to more irregular contours detected in blastomere nuclei from either treatment group (Fig. 4). Again, monopolar spindles with intense f-actin caps were evident at both low and high doses of TCDD (12/17 and 7/11 spindles, respectively, were monopolar) (Fig. 3D–F). This was further confirmed by using pixel intensity line scans to monitor the topography of cortical f-actin staining in mitotic cells (Fig. 3M and 3N). These analyses revealed equivalent intensity of f-actin around central spindles in control cells. However, as much as a five-fold increase at the apical f-actin caps was detected in cells with monopolar spindles relative to the opposite side of the blastomere (Fig. 3M and 3N). Frequently, astral-like microtubule fibers were detected between the spindle pole and cortex, accentuating the asymmetric displacement of chromosomes seen in pre-implantation embryos from treated animals (Fig. 3N).


The environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin disrupts morphogenesis of the rat pre-implantation embryo.

Hutt KJ, Shi Z, Albertini DF, Petroff BK - BMC Dev. Biol. (2008)

Nuclear profiles of compaction stage pre-implantation embryos from control and acutely exposed animals. Z-series datasets for the DNA channel were compressed into a single plane and 6 randomly selected nuclei (each from a different pre-implantation embryo) for each group (Control and 50 ng/kg and 1 μg/kg TCDD) were compared.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2254588&req=5

Figure 4: Nuclear profiles of compaction stage pre-implantation embryos from control and acutely exposed animals. Z-series datasets for the DNA channel were compressed into a single plane and 6 randomly selected nuclei (each from a different pre-implantation embryo) for each group (Control and 50 ng/kg and 1 μg/kg TCDD) were compared.
Mentions: Acute maternal TCDD exposure at the lower dose did not alter the number of compaction stage pre-implantation embryos relative to controls, but only ~52% of pre-implantation embryos from treated animals were normal (Table 1). Exposure to the higher dose of TCDD decreased the number of pre-implantation embryos, and an even lower proportion (~46%) of these pre-implantation embryos were normal (Table 1). A range of defects in nuclear and cytoskeletal integrity were observed (Fig. 3D–L), including a dose dependent loss of microtubule and f-actin staining in some blastomeres (Fig. 3J–L). Additionally, f-actin localization changed from a plasma membrane concentrated (Fig. 3C) to a more diffuse pattern of stain (Fig. 3I and 3L). In pre-implantation embryos from the 1 μg/kg treatment group, blastomeres often exhibited micronuclei (Fig. 3K, arrow) and nuclei of different sizes. Further analyses of nuclear shape revealed a range of profiles deviating from being smooth surfaced in controls to more irregular contours detected in blastomere nuclei from either treatment group (Fig. 4). Again, monopolar spindles with intense f-actin caps were evident at both low and high doses of TCDD (12/17 and 7/11 spindles, respectively, were monopolar) (Fig. 3D–F). This was further confirmed by using pixel intensity line scans to monitor the topography of cortical f-actin staining in mitotic cells (Fig. 3M and 3N). These analyses revealed equivalent intensity of f-actin around central spindles in control cells. However, as much as a five-fold increase at the apical f-actin caps was detected in cells with monopolar spindles relative to the opposite side of the blastomere (Fig. 3M and 3N). Frequently, astral-like microtubule fibers were detected between the spindle pole and cortex, accentuating the asymmetric displacement of chromosomes seen in pre-implantation embryos from treated animals (Fig. 3N).

Bottom Line: Additionally, the size, shape and position of nuclei were modified in compaction stage pre-implantation embryos collected from treated animals.We have identified the compaction stage of pre-implantation embryogenesis as critically sensitive to the effects of TCDD, while survival to the blastocyst stage is not compromised.To the best of our knowledge this is the first in vivo study to demonstrate a critical window of pre-implantation mammalian development that is vulnerable to disruption by an AhR ligand at environmentally relevant doses.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Internal Medicine, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA. huttx006@umn.edu

ABSTRACT

Background: Environmental toxicants, whose actions are often mediated through the aryl hydrocarbon receptor (AhR) pathway, pose risks to the health and well-being of exposed species, including humans. Of particular concern are exposures during the earliest stages of development that while failing to abrogate embryogenesis, may have long term effects on newborns or adults. The purpose of this study was to evaluate the effect of maternal exposure to the AhR-specific ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the development of rat pre-implantation embryos with respect to nuclear and cytoskeletal architecture and cell lineage allocation.

Results: We performed a systematic 3 dimensional (3D) confocal microscopy analysis of rat pre-implantation embryos following maternal exposure to environmentally relevant doses of TCDD. Both chronic (50 ng/kg/wk for 3 months) and acute (50 ng/kg and 1 mug/kg at proestrus) maternal TCDD exposure disrupted morphogenesis at the compaction stage (8-16 cell), with defects including monopolar spindle formation, f-actin capping and fragmentation due to aberrant cytokinesis. Additionally, the size, shape and position of nuclei were modified in compaction stage pre-implantation embryos collected from treated animals. Notably, maternal TCDD exposure did not compromise survival to blastocyst, which with the exception of nuclear shape, were morphologically similar to control blastocysts.

Conclusion: We have identified the compaction stage of pre-implantation embryogenesis as critically sensitive to the effects of TCDD, while survival to the blastocyst stage is not compromised. To the best of our knowledge this is the first in vivo study to demonstrate a critical window of pre-implantation mammalian development that is vulnerable to disruption by an AhR ligand at environmentally relevant doses.

Show MeSH
Related in: MedlinePlus